A national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy National Renewable Energy Laboratory Innovation for Our Energy Future Si Passivation and Chemical Subcontract Report NREL/SR-520-42325 Vapor Deposition of Silicon Nitride November 2007 Final Technical Report March 18, 2007 H.A. Atwater California Institute of Technology Pasadena, California NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 Si Passivation and Chemical Subcontract Report NREL/SR-520-42325 Vapor Deposition of Silicon Nitride November 2007 Final Technical Report March 18, 2007 H.A. Atwater California Institute of Technology Pasadena, California NREL Technical Monitor: R. Matson/F. Posey-Eddy Prepared under Subcontract No. AAT-2-31605-01 National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337 This publication was reproduced from the best available copy Submitted by the subcontractor and received no editorial review at NREL NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. 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Silicon Nitride Synthesis by Hot Wire Chemical Vapor Deposition:..............................1 Introduction..................................................................................................................... 1 Summary of Technical Accomplishments:..................................................................... 1 Experimental Approach .................................................................................................. 2 Radical Measurements – NH3 decomposition ................................................................ 2 Film Growth Results....................................................................................................... 3 Variation of SiH4/NH3 Flow Ratio ................................................................................. 4 Rutherford Back Scattering and Hydrogen Forward Scattering Analysis...................... 5 Annealing of Hydrogenated SiNx ................................................................................... 5 2. Solar Cell and Si Defect Passivation with HWCVD Silicon Nitride...............................7 Silicon Nitride Passivation.............................................................................................. 7 Emitter Passivation ......................................................................................................... 7 Experiments .................................................................................................................... 7 Results............................................................................................................................. 8 Pt-H Complex Formation.............................................................................................. 10 Summary of Defect and Emitter Passivation................................................................ 11 3. Thin Film Silicon Passivation in HWCVD Growth ......................................................12 Overview of Thin Film Si by HWCVD........................................................................ 12 HWCVD Gas Phase Species Characterization ............................................................. 12 Rates for Surface Kinetic Processes ............................................................................. 13 A Phase Diagram for Morphology and Properties of Low Temperature Deposited Polycrystalline Silicon Grown by Hot-wire Chemical Vapor Deposition.................... 15 Minority Carrier Lifetimes of HWCVD Films............................................................. 19 HWCVD Si Film Passivation ....................................................................................... 22 Microstructure and Passivation Effects on Open Circuit Voltage................................ 22 HWCVD Growth and Morphology .............................................................................. 23 Open-Circuit Voltage.................................................................................................... 23 Surface Passivation ....................................................................................................... 24 References..........................................................................................................................26 Personnel Associated with Subcontract.............................................................................28 Researchers: .................................................................................................................. 28 Collaborators:................................................................................................................ 28 Publications under subcontract ..........................................................................................29 PhD Theses: .................................................................................................................. 29 Journal Publications:..................................................................................................... 29 Presentations under Subcontract........................................................................................31 Honors and Awards under Subcontract .............................................................................33 iii List of Figures Figure 1. FTIR transmission spectra of films grown under different SiH4/NH3 flow ratios (indicated in %)..............................................................................4 Figure 2. FTIR spectrum at various annealing temperature for a film grown with 8% SiH4 in NH3 ...............................................................................................9 Figure 3. Creation of Pt-H complexes in bulk Si by annealing of hydrogentated SiN3 layer.......................................................................................................10 Figure 4. Photomicrograph of silicon nitride-passivated String Ribbon solar cell; white line depicts position of the wire array during hot wire CVD growth ..11 Figure 5. Rates of interest for wire surface kinetic processes .......................................14 Figure 6. Phase diagram of HWCVD films grown at 50:1 hydrogen dilution with 4% SiH4 in He................................................................................................17 Figure 7. Plan-view TEM of HWCVD epitaxial film (T=3000C) on SNSPE template..........................................................................................................18 Figure 8. LLI and HLI minority carrier lifetimes of HWCVD films on Si(100) as measured by RCPCD .....................................................................................19 Figure 9. LLI and HLI minority carrier lifetimes on SNSPE templates .......................19 Figure 10. Silicon to oxygen ratio in the first monolayer of growth as a function of substrate temperature for dilute silane growth at 50:1 hydrogen dilution and epitaxial thickness ...................................................................................20 Figure 11. Silicon to oxygen ratio in the first monolayer of growth as a function of R for pure silane growth using the deposition conditions in Table 4 along with the Raman crystalline % ..............................................................21 Figure 12. Schematic of proposed photovoltaic device incorporating epitaxial Si growth on a large-grained polycrystalline template fabricated by SNSPE....22 Figure 13. Cross-sectional TEM of growth morphology at various hydrogen dilutions..........................................................................................................23 Figure